There are generally multidimensional methods for increasing a transmission rate of a communication system, for example, increasing transmit power, increasing system bandwidth and increasing spectrum efficiency. According to Shannon's Capacity Formula, increasing system bandwidth is a relatively easy method with the most significant effect. Therefore, the system bandwidth is increased as much as possible for most communication systems. On the other hand, since spectrum resources for wireless communication systems are rare and non-renewable, dedicated frequency bands are very expensive. At present, a mobile communication system operator can effectively operate a mobile communication network such as a Long Term Evolution (LTE) network if the operator can obtain a bandwidth of 100 MHz.
How to effectively use the spectrum resources as much as possible is an important direction for wireless communication systems. Further, there are two methods for improving the utilization of spectrum resources in this direction. One is to improve the spectrum efficiency by means of a physical layer (PHY), for example, improving the spectrum efficiency by increasing a modulation order, increasing a coding rate by using better code words, and forming parallel paths by using space resources in a manner of multiple input multiple output (MIMO). The other one is to improve the efficiency of utilization of spectrum resources by a link or a network, by designing mechanisms such as media access control (MAC) layer scheduling and channel access.
The present application mainly refers to the latter one, that is, an effective solution to utilize spectrum resources in a contention-based access network. For example, in a current Wireless Fidelity (WiFi) system, a data transmitting end uses a dynamic Request to Send/Clear to Send (RTS/CTS) method to better learn which sub-channels are idle and available currently. Specifically, RTSs are sent in multiple contiguous sub-channels to request the use of the sub-channels; the receiving end, upon receipt of an RTS on a corresponding sub-channel, replies with a CTS after determining that the channel is idle; and the transmitting end learns the specific channel idleness state based on the received CTS. In order to enhance reliability of the mechanism, bandwidth information is carried in both the RTS and the CTS to indicate a bandwidth currently requested. For example, there are four contiguous channels 1, 2, 3, and 4, where channel 3 is busy and the other channels are idle. In the solution, limited bits (3 bits) are used to indicate the bandwidth (BW); therefore, neither the receiving end nor the transmitting end supports a discrete multi-channel signal. In this case, if the receiving end determines that channel 3 is busy, the receiving end can reply with a CTS on only channel 1 and channel 2 even though channel 4 is idle. The transmitting end transmits data to the receiving end on channel 1 and channel 2 based on the CTS fed back by the receiving end.
In addition, since 3 bits are used to indicate BW in the solution, a contiguous bandwidth which can be indicated by the 3 bits is extremely limited, which is specifically described as follows: With reference to BW and a location of a primary channel, the transmitting end can communicate with the receiving end in only five modes: 20 MHz of the primary channel, 40 MHz including the primary channel, 80 MHz including the primary channel, contiguous 160 MHz including the primary channel and non-contiguous 160 MHz including the primary channel, and a frequency point of a secondary channel (some channels which are not the primary channel) must be higher than a frequency point of the primary channel, otherwise these possible combinations cannot be indicated.
In the foregoing solution, 3 bits are used to indicate BW, and combinations of non-contiguous sub-channels cannot be indicated by the 3 bits in view of a location relationship of frequency bands. Even if the foregoing solution is applied to contiguous sub-channels, not all contiguous bandwidth combinations can be indicated. For example, a bandwidth of 60 MHz consisting of contiguous sub-channels cannot be indicated. In conclusion, the foregoing solution for indicating sub-channels is greatly limited and cannot indicate all combinations of sub-channels.